<template>
    <ul class="list">
        <li class="item"
            v-for="item of letters"
            :key="item"
            :ref="item"
            @touchstart="handleTouchStart"
            @touchmove="handleTouchMove"
            @touchend="handleTouchEnd"
            @click="handleLetterClick"
        >
        {{item}}
        </li>
    </ul>
</template>
<script>
export default{
    name:'CityAlphabet',
    props:{
        cities:Object
    },
    computed: {
        letters () {
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    data(){
        return{
            touchStatus:false,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change',e.target.innerText)
        },
        handleTouchStart () {
            this.touchStatus = true

        },
        handleTouchMove (e) {
            if(this.touchStatus) {
                if(this.timer){
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(()=>{
                    const touchY = e.touches[0].clientY-79
                    const index = Math.floor((touchY-this.startY)/20)
                    if(index>=0 && index <= this.letters.length) {
                        this.$emit('change',this.letters[index])
                    }
                },16)

            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>
<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
